GIF 1
Go to transform data > on the right of the power query page, click on the Class Management table > duplicate the classname column and split by delimiter.
GIF 2
Remove the first section of the splitted columns > split the other column by delimiter > Replace values as shown below
GIF 3
Continue replacing value so it would be easier to change data type to 'date'
GIF 4
Change column's data type to date and remove unnecessary columns.
GIF 5
Close and apply changes
GIF 6
Sort ClassName column by the new calculated column
Difference between calculated column and calculated measure: